Question

In binary data transmission, DPSK is preferred over PSK because

• A. more protection is provided against impulse noise
• B. for a given energy per bit, the probability of error is less
• C. the 180° phase shifts of the carrier are unimportant
• D. a coherent carrier is not required to be generated at the receiver

Hint:

The "D" in DPSK stands for Differential. This means information is in the difference between symbols. This makes the receiver "non-coherent" because it doesn't need an external coherent reference carrier, simplifying its design.

Answer 1

The Correct Option is D

Step 1: Understand PSK (Phase Shift Keying). In coherent PSK, the receiver must generate a local carrier wave that is perfectly synchronized in phase with the incoming carrier wave. This is used as a reference to determine the phase of the received signal. Generating this coherent carrier is complex and adds to the cost and complexity of the receiver.
Step 2: Understand DPSK (Differential Phase Shift Keying). In DPSK, the information is encoded in the difference in phase between consecutive symbols, not in the absolute phase. For example, a '1' might be represented by no phase change, and a '0' by a 180° phase change. The receiver demodulates the signal by comparing the phase of the current symbol with the phase of the previous symbol.
Step 3: Compare the two. Because DPSK uses the previous symbol as its own phase reference, it does not need a separate, locally generated coherent carrier. This simplifies the receiver design significantly. While DPSK has a slightly higher bit error rate than ideal coherent PSK for the same SNR, its major advantage is the avoidance of complex carrier recovery circuits.